The study will examine the interaction between dietary fiber and flax, a known source of lignan precursors, on urine and serum sex steroid metabolism and urinary lignan concentrations in premenopausal women. Twenty four women will be recruited in anticipation that twenty will finish. Subjects will consume the followign dietary treatments in a randomized order: 1. a control diet, low in dietary fiber and lignans 2. a wheat bran diet, high in dietary fiber and low in lignans 3. a flaxseed diet, low in dietary fiber and high in lignans, and 4. a wheat bran plus flaxseed diet, high in dietary fiber and lignans. Each diet will be consumed for two cycles with biological sample collections in the second menstrual cycle of each treatment.